There is known a one-component coating composition prepared by using a mixture of silicon carbide and a phosphate as a binder. This composition may be applied to, for example, the wall of an industrial furnace to improve its thermal efficiency. However, the refractory coating formed by this composition has a number of disadvantages. At a high temperature of, say, 1,000.degree. C. or above, it is not only likely to peel off the furnace wall, but also tends to cause the surface layers of bricks to peel off the wall. Even in a medium temperature range, chemical reactions and thermal stress develop both at the contact surface and within the refractory material soaked with the binder, depending on the refractory material. They cause structural spalling and embrittlement, resulting in the cracking and peeling of the coating. Especially in the case of highly porous refractories having a low coefficient of elasticity, their low compressive strength tends to cause the disintegration of the refractories due to the concentration of stress in the area between the portion of which the thermal and physical properties have been changed as a result of the contact or impregnation of foreign material, and the remaining portion.